Strangles: Understanding Equine Distemper and Purpura Haemorrhagica

Posted November 29, 2012

One of the most alarming of infectious diseases in the equine
industry is Strangles, which is noted for the characteristic large
swelling of lymph nodes under the jaw or in the throat area.
Sometimes the node enlargement progresses to the point of
interfering with airway or swallowing functions creating a concern
that the patient might strangle.

Strangles, also known as equine distemper, is caused by a
bacterial infection of the highly infectious Streptococcus equi
(Strep equi). It most commonly affects young horses, generally two
years of age or less. Although the disease is potentially fatal,
the mortality rate is generally less than 10 percent. The morbidity
rate, however, is quite high due to the infectious nature of the
germ and its ability to survive once infected horses contaminate
the environment. The disease has an incubation period ranging from
a few days to two weeks. Therefore, minimum isolation time of two
weeks is recommended with horses that have been exposed, or horses
having an unknown history for biosecurity purposes.

"We see it so commonly in young horses when the germ is found in
endemic areas; the younger animals often lack adequate immune
protection" said Dr. Glennon Mays, clinical assistant professor at
the Texas A&M College of Veterinary Medicine & Biomedical
Science (CVM). "That means that once a location is contaminated
with Strangles, we often see it reappear in the horse population
because the bacterium is located in that environment. When horses
are born or brought to that location, if they don't have protective
immunity, they become infected. "

The Strep equi germ can survive in contaminated soil, water
troughs, feed buckets, and tack. The germ can even be transferred
by people from one location to another. Direct transmission between
horses occurs through contaminated mucus excretions of the infected
horse to the naïve horse. Contaminated horses may shed the germ for
two to three weeks.

Infected horses can exhibit several signs, such as general
depression and dull behavior, runny nose or eyes and fever. The
classic symptom of the infection is swollen lymph nodes beneath the
jaw or throat areas or in other external and/or internal body
locations. Lymph nodes will usually swell two to three days after
infection, and horses will be able to spread disease for
approximately two to three weeks after clinical signs appear.

"These lymph nodes swell in reaction to the infection, and often
develop into large pus formations," Mays said. "After swelling,
when the nodes soften, it is often therapeutic to drain the nodes
by surgical incision. But this requires great caution since large
blood vessels are often in close proximity. Care to contain the
recovered pus is necessary because it can be very contaminating
wherever it collects. The lymph nodes really serve as an area of
collection of the bacteria and a concentration point of the
infection."

"You don't want that fluid getting into the soil, or on objects
that will come in contact with uninfected horses," Mays said.
"Remember that the person handling the infected horse or the
infected material coming from the horse can become a vehicle for
spreading the disease."

In addition to relieving the swelling of glands, veterinarians
will typically administer supportive care, such as
anti-inflammatory medications, to horses that retain an adequate
appetite, hydration status, and don't display difficulty
breathing.

Some patients may experience high fever spikes (103 F or more)
and require more aggressive therapy. In these instances,
administration of antibiotics, electrolyte fluids, and
anti-inflammatories become necessary. Additional products believed
to stimulate the immune system are sometimes incorporated into the
therapeutic plan, however, many equine practitioners choose against
initiating antimicrobial therapy unless the patient is fevered,
depressed, and listless to the point of not eating and drinking
adequately.

Mays explained that in some cases Strangles can develop into a
clinical presentation called Purpura Haemorrhagica. Purpura causes
vasculitis in the extremities resulting in painful swelling of the
legs due to acute inflammation of peripheral blood vessels. The
legs become tender and sore because circulation is impaired. Horses
that develop this condition are either infected with Strangles and
progress to the purpura stage, or were previously exposed to the
germ without developing an infection.

"The reason behind this development is poorly understood, "Mays
said. "But horses that develop purpura are extremely depressed and
actually show more clinical signs of illness - essentially sicker
than with Strangles alone."

The vasculitis in the legs can significantly prolong recovery,
and can be severe enough that the swelling permanently damages
musculoskeletal structures. Laminitis is not an unusual resulting
chronic condition. Complications from purpura can produce
career-ending results for performance horses. Purpura can also
become fatal if not treated in a timely or effective manner.

The best defense against Strangles is to create a barrier
through biosecurity. Avoid transporting young horses into
contaminated or endemic areas. Isolate horses of unknown exposure
history for a minimum of two weeks to prevent possible exposure of
disease to other animals. Do not bring horses displaying signs of
illness into contact with healthy horses. Remember, the infection
can be transferred on clothing, tack, vehicle tires, or hands. Due
to Strangles' extremely contagious character, seek veterinary care
immediately if suspected. . Often, the veterinarians prefer to
examine the animal away from their clinic to avoid
contamination.

Vaccines have been available for decades, but remain a contested
topic for recommendation. Mays explained that many veterinarians
approach vaccination recommendation with caution. "Strep vaccines
historically have more potential for reactive properties than other
equine biological products. Many practitioners express concern for
an increased frequency of post-vaccination complications with
Strangles vaccine," Mays said.